Folding support structure for offshore drilling platforms



June 30, 1970 E O. 3,517,516

FOLDING SUPPORT STRUCTURE FOR OFFSHORE DRILLING PLATFORMS Filed July 51,1968 s Sheets-Sheet 1 FIG. 2

INVENTOR'.

ROBERT G. BEA

R. G. BEA

June 30, 1970 FOLDING SUPPORT STRUCTURE FOR OFFSHORE DRILLING PLATFORMS5 Sheets-Sheet 2 Filed July 51, 1968 INVENTORI ROBERT G. BEA

June 30, 1970 R. G. BEA 3,517,516

FOLDING SUPPORT STRUCTURE FOR OFFSHORE DRILLING PLATFORMS Filed July 31,1968 5 Sheets-Sheet 5 ROBERT e. BEA

FOLDING SUPPORT STRUCTURE FOR OFFSHORE DRILLING PLATFORMS Filed July 51,1968 R. G. BEA

June 30, 1970 5 Sheets-Sheet 4 FIG.

FIG.

INVENTORI ROBERT G. BEA I June 30, 1970 R. 5. BEA

FOLDING SUPPORT STRUCTURE Filed July 31, .1968

FOR OFFSHORE DRILLING PLATFORMS 5 sheets-sheet 5 I NVENTOR'.

ROBERT G. BEA

United States Patent i 3,517,516 FOLDING SUPPORT STRUCTURE FOR OFFSHOREDRILLING PLATFORMS Robert G. Bea, Houston, Tex., assignor to Shell Oilgonlipany, New York, N.Y., a corporation of New Filed July 31, 1968,Ser. No. 749,182 Int. Cl. E02b 17/02 US. Cl. til-46.5 8 Claims ABSTRACTOF THE DISCLOSURE An offshore drilling structure having a buoyant,selectively floodable base unit and a plurality of buoyant, selectivelyfloodable leg units pivotally attached to said base unit whereby thestructure can be set-up by towing the entire assembly on the surface ofa body of water to a predetermined offshore location, lowering theassembly to the water floor by flooding the base unit and legs, andpivoting the leg units upwardly to form a composite offshore drillingstructure.

This invention relates to portable support structures for deep wateroffshore drilling platforms.

It is well known in the prior art to prefabricate support or towerstructures for drilling platforms at inland or coastal locations andfloat the completed structure down a river or through a channel out tothe sea or gulf to the desired location where it is sunk in an uprightposition. When in place, the drilling platform, derrick structure, drawworks and other necessary equipment are positioned atop the towerstructure.

The main load-bearing columns of these structures are usually tubularsteel pipes of a relatively large diameter. The ends of these tubularcolumns are capped so that each column constitutes a buoyant, watertightvessel. This is for the purpose of providing inherent flotation to thestructure so it may be towed over the surface of the water to thelocation of use.

As the quest for oil has progressively pushed the drilling locationsinto the deeper water covering the outer limits of the ContinentalShelf, it has been necessary to build these tower structures larger andhigher to accommodate the depth of the water and the wind and waveforces imposed in the open sea. This necessary increase in size of thestructures has had the consequent effect of increasing the draft of thestructures as they are laid over on their sides to be floated from theconstruction point to the drilling location. Many of these constructionsites are located far inland on rivers such as the Mississippi. Theserivers are relatively shallow and cannot accommodate a deep draftvessel, hence presenting one problem sought to be solved by thisinvention.

It is therefore an object of this invention to provide a deep waterdrilling support structure that may be constructed at a shipyard andcarried through shallow waterways to the sea.

It is another object of this invention to provide a floatable towerstructure having a very shallow draft.

It is still another object of this invention to provide a prefabricatedfloatable tower structure in which each structural element buoyantlysupports little more than its own weight.

It is a further object of this invention to provide a partiallydisassembled, prefabricated tower structure that may 3,517,516 PatentedJune 30, I970 be floated to location where assembly may be quickly andeasily completed. I

It is an additional object of this invention to provide a prefabricatedfloatable tower structure which may be recovered and moved to anotherlocation when it is utility at a first location is complete.

Another object of this invention is to provide a foldable towerstructure in which the folding legs thereof are quickly and easilyassembled together as a unitary structure.

Still another object of this invention is to provide means for securingthe folding legs of a transportable, deep water tower structure togetherat great depths with means that is manipulated into position at or nearhe surface.

These and other objects will be readily seen from the following detaileddescription when taken in conjunction with the accompanying drawingswherein:

FIG. 1 is a diagrammatical side elevational view of the articulatelyassembled floating tower structure as it is being towed over a body ofwater to location;

FIG. 2 is a diagrammatic view of the tower structure in the initialerection stage;

FIG. 3 is a diagrammatic view of the tower structure in a more advancederection stage;

FIG. 4 is a diagrammatic plan view of the tower structure as erectionapproaches completion;

FIG. 5 is a diagrammatic view of the completed tower structure equippedfor drilling;

FIG. 6 is a sectional view of the tower structure shown in FIG. 5 takenalong line 66;

FIG. 7 is a sectional view of the tower structure shown in FIG. 5 takenalong line 77;

FIG. 8 is a sectional view of the tower structure shown in FIG. 5 takenalong the line 8-8;

FIG. 9 is a sectional view of the hinge structure which joins the legunit with the base;

FIG. 10 is a sectional view of the hinge structure shown in FIG. 9 takenalong line 10-10;

FIG. 11 is an alternative embodiment for the structure shown in FIG. 7;

FIG. 12 is a sectionalized detail of connecting carrier lower endsecured in place within its respective guide track; and

FIG. 13 is a partial cross section of the guide trace showing means forsealing the'longitudinal slot therein.

Broadly, the tower structure of this invention is preferably dividedinto at least three segments, a base 10 and two leg units 20 and 20a.One end of each leg unit is secured to respectively opposite ends of thebase unit by an articulating connection such as a hinge. Although onlytwo leg units are shown and preferred, it is, of course, possible toprovide four leg units, each one articulately connected to a respectiveside of a rectangular base structure.

Another possible base configuration for this invention is that of atriangular base. In the case of a triangular base, there would be threeleg units, each hingedly connected along the edge of a base trianglelying in the plane of the water surface.

With reference to FIGS. 5, 6 and 8, each leg unit 20 and 20:: comprisestwo primary columns 21 and 22 which are of suflicient length to extendfrom the marine floor 72 to a height of, for example, approximately feetabout the surface 76 of a body of water 70. The water depth at alocation of drilling activity may be 400 feet, for example.

o The primary columns are secured directly together by a plurality ofcross spanners 23 disposed at several vertically spaced locations of,for example, 100 feet, to form a lattice structure. Additionally, at theends of the primary columns intended to extend above the water surface,a platform beam 51 is rigidly secured between said primary columns 21and 22 respective to each leg unit. The primary columns 21 and 22 may,for example, be constructed of 12-foot diameter steel tubing. The crossspanners 23 may, for example, be of 4-foot diameter steel tubing.

From the lattice structure comprising the primary columns and crossspanners, there is provided gabled spanners such as 24'and 25. The gablespanners 24 and 25 intersect to form, with the cross spanner 23, atriangular cross section for the leg unit 20 (see FIG. 6). Each apexformed by the intersection of gable spanners 24 and 25 is supported andreinforced by cross bracing 29 (FIG.

Supported by the apex of the gable spanners 24, 24a, 25

and 25a, as shown in FIGS. 5-7, are guide tracks 30 and 30a which shouldextend from at least the surface level of the structure down past thelowermost gabled spanner 24. Each of the guide tracks 30 and 30a shownin FIGS. 5-7 are tubular structural members having a slot 31 in the Wallthereof extending substantially the entire length. The lower ends of theguide tracks 30 and 30a may be provided with abutment means such as acrossbar 32 shown in FIG. 12.

Secured between the gabled spanners 24 and 25 along the length of eachleg unit is a cluster of conductor pipes 34 and 34a. Each of theseconductor pipes constitutes drill string guides and is sized accordingto the programmed equipment necessary to the drilling and completion ofindividual wells which are to be drilled therethrough and angleddirectionally therefrom.

Alternatively, the guide tracks respective to each leg unit may take theform of channel members 45 having guide ways 46 extending partiallyacross the channel opening from each channel leg leaving a longitudinalspace 47 therebetween as shown in FIG. 11.

In connection with the guide tracks 30 and 30a. but fabricated as aseparate structure is a connecting carriage 54 comprising, in theembodiment of FIGS. 5-7, two tubular carriers 55 and 55a. The carriers55 and 55a are interconnected along their length, which is at least aslong as the guide tracks 30 and 300, with run members 56. If theintended use of the completed tower structure calls for permanentpositionment, the carriers 55 and 55a may have their ends plugged with apipe cap 57 and perforated along the length of the carrier withapertures 58 as shown in FIG. 12. Also, when the contemplated placementof the tower structure is to be permanent, the slot 31 along the lengthof the guide tracks 30 and 30a is loosely sealed with overlappingwelting 59.

To provide sufficient spacing between the platform beams 51 for thestable positionment of the operating platform 50 thereacross and torigidly secure the two leg units together in the upright position duringthe initial assembly stage, spacer means 37, shown in FIG. 5, forexample, have been provided at the ends of the leg units and 20a. Theportion of the spacer means secured to each leg unit constitutes half ofa diagonally reinforced box truss. The two halves are secured togetherwith mating flanges 38.

The base unit 10, shown in FIG. 8, is preferably in the form of a squarehaving two sides, the primary beams 11 and 12, constructed of, forexample, 8-foot diameter steel tubing, and the other two sides, thesecondary beams 13 and 14, constructed of 38-inch diameter tubing, forexample. The base square 10 is reinforced by a truss structure 15constructed of, for example, 4-foot diameter steel tubing. The trussstructure 15 supports at the center a template plate 16 having apertures17 of a size at least equal to the inside diameter of the conductortubes 34. The apertures 17 are positioned on the template plate 16 inalignment with the bores of conductor tubes 34 with the legs 20 and 20aare in the raised, operative position,

The leg units 20 and 2011 are secured to the base unit 10 byarticulating joints shown at FIGS. 9 and 10. Each articulating joint hasa journal pin 42 mounted on a hydraulic ram 43 for reciprocal movementwithin the secondary beams 13 and 14 and at each end of the primary beammembers 11 and 12 of the base unit 10. The journal pin 42 mates with ajournal sleeve 41 mounted in the bottom end of the primary columns 21and 22. The fluid power for the hydraulic rams 43 is received from anauxiliary barge unit 60 or a portable power unit (not shown) mounted ata convenient location on the base unit 10.

All construction tubing excepting the guide tracks 30' and 30a ispreferably sealed watertight, either by construction design or by meansof end caps 44, for example, on the primary column 21 shown in FIG. 8.It should be noted, however, that although it is intended that each ofthe basic units of the structure should be buoyantly selfsupporting inthe water, this does not preclude the possibility of using auxiliaryflotation means to which the units may be attached for whole or partialsupport. By attaching pontoons or other auxiliary flotation means, thestructure may be made to gain a still more shallow draftthan wouldotherwise be possible. Buoyancy of the structure may also be changed byaltering the outside diameterthickness ratio of the individualstructural tubing elements. In other words, for structural elementshaving the same load-bearing properties, the unit specific gravity wouldbe greater for a tubular element having a smaller outside diameter butgreater wall thickness. For this reason, unusual circumstances of draftand buoyancy may be met by constructing the primary columns from verylarge diameter but thin-walled tubing having load-bearing capacitiesgreatly in excess of what is necessary.

Extending throughout the internal length of primary columns 21 and 22are provided piling sleeves 39. The piling sleeves 39 extend through theend caps 44 and a short distance therebeyond. The piercing point of thepiling sleeves 39 through the ends caps 44 is also made watertight. Theopposite ends of the piling sleeves 39 may also be temporarily cappedand made watertight until at such later time as they are ready toreceive the pilings 40.

The basic units of the tower structure comprising the base 10 and thetwo leg units 20 and 2011 may be conveniently assembled at an inlandshipbuilding or drydock facility. Since each unit is preferablyconstructed as 'a buoyant vessel, the three units may thereafter belaunched in the carrier waterway where they are assembled in the mannershown by FIG. 1. This assembly operation is made relatively simple bythe hydraulic-ram powered tapered journal pins 42. Since the pins 42 areprovided with a reduced diameter tapered end, it is only necessary tobring each leg unit within such reasonable proximity of the pin 42 as toallow the pin 42 to enter the confines of the sleeve 41. When the pinand sleeve are sufiiciently aligned, the ram 43 is energized so as toforce the pin 42 home within the sleeve 41.

When assembled, the three units present a low profile to the forces ofwind and wave action and also have a shallow draft, thereby making itnavigable in shallow rivers and canals. In this manner, the floatingstructure is towed, as by a tug 75, to the desired drilling location onthe outer limits of the continental shelf where the water depth may be400 feet or more.

It is also possible, of course, to tow each unit separately to thedrilling location where it will be assembled in the manner describedabove by aligning the journal sleeves 41 with the pins '42 and rammingthe latter into position with the hydraulic motors 43. This lattermethod of individual transport of each unit to the location and assemblythereat may be desirable when short-radius turns are anticipated on theway to location. However, sea conditions will present a greaterhindrance to the alignment of the pin 42 in the sleeve 41 than would beencountered by such assembly in a river or canal.

When the articulated structure has arrived over the desired location, anauxiliary barge 60 is moved into position adjacent the base unit (FIG.2). Control cables 62 are secured to the opposite ends of the base unit10 and to winches secured to the auxiliary barge 60. Also from theauxiliary barge 60 are connected ballast control lines 66, 66a and 67which are at their other ends connected to water pumps in the barge 60.

At the outer end of each leg unit 20 and 20a tugs 75 and 75a secure towcables 76 and 76a. The barge 60 is held in lateral position with anchorlines 61 and 61a.

At the desired moment, the ballast tanks internally of. the basestructure 10 are filled with water pumped through the base ballastcontrol line 67. Simultaneously, the internal voids of the legstructures 20 and 20a are flooded with water through the leg ballastcontrol lines 66 and 66a. The result of such flooding is to cause theplatform and the hinged ends of the leg units 20 and 20a to sink towardthe marine floor 72. In order to control the attitude of sinking, bothcontrol cables 62 are let out from the barge 60 at the same rate. Theobjective of control lines 62 is to keep the platform 10 in a horizontalattitude as it approaches the marine floor. Also effective to controlthe rate of sinking and the attitude of the plat form 10 is the tensileeifect of the tugs 75. The tugs 75 pull in opposition to one another tolighten the corrective loads imposed on the control lines 62 as theentire base structure approaches the bottom and the legs 20 and 20apivot to an upright position.

When the base unit 10 is firmly positioned on the marine floor 72 (FIG.3) erection cables 63 are threaded through the sheaves 64 and 64alocated on the respective surface ends of leg units 20 and 20a. Atension line 65 extends from the erection cables to a power winchlocated on the barge 60. As the tension cable 65 is drawn up, the legunits 20 and 20a are pulled together into the upright position as shownin FIG. 3. In the upright position the flanges 38, located on the endsof the spacers 37, are secured together, thereby providing the structurewith a modicum of rigidity in the proper alignment position.

At this juncture of the assembly, the connecting carriage 54 is insertedand slid down through the guide tracks 30 and 30a until the lower endthereof rests against the abutment member 32. In the case of very hightower structures where the guide tracks are proportionally long, theconnecting carriage 54 may be fabricated on location by joining as byWelding a plurality of short lengths of connecting carriage that aremore conveniently handled and hoisted into place. When the alternativeguide track embodiment of FIG. 11 is used, the connecting carriage maytake the form of a structural I or H beams 48.

If, as suggested above with respect to FIG. 12, the tower structure isto be permanently located, the carriers 54 and 54a may be permanentlysecured in place by pumping cement 33 down the bore of the carrier tubesto be extruded through the perforations 58 into the annulus between theouter and inner walls of the carriers and guide tracks, respectively.The welting '59 provides sufficient sealing means along the slot 31which is necessary to longitudinally, slidably accommodate the rungs 56as the connecting carriage is being slid into position.

Next in the order of assembly, an operating platform 50 may beconstructed across the platform beams 51 upon which a doghouse 52 andderrick structure 53 may be erected. It is to be understood that otherarrangements of control lines and erection cable may be employed inerecting the structure of the present invention.

In order to firmly secure the tower structure to the ocean floor,pilings 40 are extended through the piling sleeves 39 and driven deeplyinto the marine floor and cemented in position.

The structure disclosed above may be used to drill many wells from asingle location. For this purpose, the multiplicity of conductor pipes34 is provided as drill string guides from the operating platform downthrough the truss network of the tower structure. A separate well isdrilled through each conductor by directionally drilling each accordingto a predetermined radial pattern.

When the tower structure has exhausted its utility as a drillingplatform, it will usually be left permanently in place where it is usedto mount such equipment as is necessary for the continuous productionand control of the oil and other minerals produced from all the wellsterminating thereat. However, should it be desired to do otherwise, itis possible to recover the entire tower structure for movement toanother location. This is accomplished by merely dismantling andremoving the platform 50 and superstructure, removing the connectingcarriage 54, separating the flanges 38, severing each piling with aninternal pipe cutter and pumping the ballast water from the internalspaces of the base and leg units. The tower structure will then be freeto rise to the surface where it can be towed by tugboat to the newlocation.

I claim as my invention:

1. An offshore drilling structure comprising:

a floatable base unit having variable ballast means;

a plurality of floatable leg units having variable ballast means andincluding column means having spanner means projecting laterally fromsaid column means;

hinge means operatively associated with said units and having horizontalpivot axes securing one end of said leg units to an edge of said baseunit;

longitudinal guide means comprising track members fixedly secured tosaid laterally projecting spanner means along a substantial portion ofthe length of said leg units in such a position that when said leg unitsare pivoted to the upright operative position guide means for eachrespective leg unit extend substantially parallel with, laterally spacedfrom, and in close proximity of guide means for another leg unit; and

carriage means simultaneously slidably received by guide meansrespective to at least two of said leg units whereby said leg units areeitectively secured together along substantially the full length of thecarriage means.

2. Apparatus as described by claim 1 wherein each of said guide meanshas slot means along the length thereof on the side adjacent saidcooperative guide means, said slot means adapted to slidably receiveinterconnecting structural means of said carriage means to secure therespective leg units together.

3. Apparatus as described by claim 2 wherein said carriage means is astructural I-beam member and the interconnecting structural means is theweb of said I- beam.

4. Apparatus as described by claim 2 wherein said guide means aretubular track members and said carriage means comprises tubular membershaving outside diameters less than the inside diameters of therespective guide means tubular track members, each carriage meanstubular member being concentrically received by respective guide meanstubular track members, said interconnecting structural means comprisinga plurality of structural bracing members secured at opposite ends to atleast two cooperative carriage means tubular members concentricallydisposed in the guide means tubular track members of at least tworespective leg units.

5. Apparatus as described by claim 4 wherein each of said carriage meanstubular members are perforated along the length thereof and capped atthe bottom end, said carriage means being secured in place in said guidemeans by cement.

-6. Apparatus as described by claim 1 wherein each of said hinge meanscomprises a journal pin mounted on one of said units, said journal pinbeing axially reciprocal by power means and a journal sleeve mounted onthe other of said units, receiving said journal pin when same is axiallyextended.

7. Apparatus as described by claim 1 additionally comprising anchormeans extending telescopically through said one end of said leg unitswhereby said structure is secured to the earth.

8. Apparatus as described by claim 1 wherein said leg units eachcomprise a truss structure of diminishing triangular cross-sectionalarea along the length thereof from said one end to the other end, twolongitudinal edges of said truss structure being primary tubular supportcolumns and interconnecting respective base angles of longitudinallydisplaced triangular cross sections, said guide means passinglongitudinally through the respective apex angles of said cross sectionswhereby the base plane common to said primary support columns stands atbatter and substantially includes an edge of said base unit when saidleg unit is in an upright, load-supporting 641,838 1/1900 Cavanagh 28720.92 3,253,417 5/1966 Manning 61-465 3,348,459 10/1967 Harvey 52-58 96JACOB SHAPIRO, Primary Examiner U .8. C1. X.R.

